Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, 430070, PR China; College of Horticulture & Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, PR China.
Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, 430070, PR China; College of Horticulture & Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, PR China; Department of Horticulture, Muhammad Nawaz Shareef University of Agriculture, Multan, 60000, Pakistan.
Plant Physiol Biochem. 2021 Mar;160:211-217. doi: 10.1016/j.plaphy.2021.01.019. Epub 2021 Jan 21.
Citrate is an important intermediate product for the biosynthesis of several metabolites in plants. As two important organs of the citrus plant, fruits and leaves have their own metabolites characteristics; among them, citrate is normally high in fruit juice sacs (JS) and low in leaves. In this study, citrate content and transcript levels of citrate synthesis, transport, storage, and utilization related genes were compared between leaves and fruit JS of Citrus reticulata cv. 'Huagan No. 2', C. grandis cv. 'Hirado Buntan', and C. sinensis cv. 'Anliu'. Results indicated that the citrate content in fruit JS was significantly higher than in leaves of each cultivar. Only the relative mRNA levels of a P-type proton pump gene, CsPH8, was significantly lower in leaves than in fruit JS of three citrus cultivars, while other genes related to citrate biosynthesis, transport, storage, and utilization were highly expressed in leaves as compared to fruit JS. Furthermore, CsPH8 transient and stable transformation in leaves indicated that the change in citrate content is highly consistent with the change of CsPH8 transcript levels. Taken together, our results strongly suggest that the low accumulation of citrate in citrus leaves is mainly due to the low expression level of CsPH8; additionally, the high level of expression of citrate-utilizing genes would prevent citrate accumulation in the leaf organ.
柠檬酸是植物中几种代谢物生物合成的重要中间产物。作为柑橘植物的两个重要器官，果实和叶片具有各自的代谢物特征；其中，柠檬酸通常在果实汁囊 (JS) 中含量较高，而在叶片中含量较低。在这项研究中，我们比较了‘华柑 2 号’、‘Hirado Buntan’甜橙和‘暗柳橙’叶片和果实 JS 中柠檬酸合成、转运、储存和利用相关基因的柠檬酸含量和转录水平。结果表明，果实 JS 中的柠檬酸含量明显高于每个品种叶片中的含量。只有 P 型质子泵基因 CsPH8 的相对 mRNA 水平在三个柑橘品种的叶片中显著低于果实 JS，而柠檬酸生物合成、转运、储存和利用相关的其他基因在叶片中的表达水平明显高于果实 JS。此外，CsPH8 在叶片中的瞬时和稳定转化表明，柠檬酸含量的变化与 CsPH8 转录水平的变化高度一致。综上所述，我们的结果强烈表明，柑橘叶片中柠檬酸积累较少主要是由于 CsPH8 表达水平较低；此外，柠檬酸利用基因的高水平表达可以防止柠檬酸在叶片器官中积累。
